Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
Phys Rev Lett. 2011 Mar 18;106(11):115703. doi: 10.1103/PhysRevLett.106.115703. Epub 2011 Mar 16.
The Green-Kubo equation relates the macroscopic stress-stress correlation function to a liquid's viscosity. The concept of the atomic-level stresses allows the macroscopic stress-stress correlation function in the equation to be expressed in terms of the space-time correlations among the atomic-level stresses. Molecular dynamics studies show surprisingly long spatial extension of stress-stress correlations and also longitudinal and transverse waves propagating in liquids over ranges which could exceed the system size. The results reveal that the range of propagation of shear waves corresponds to the range of distances relevant for viscosity. Thus our results show that viscosity is a fundamentally nonlocal quantity. We also show that the periodic boundary conditions play a nontrivial role in molecular dynamics simulations, effectively masking the long-range nature of viscosity.
格林-久保方程将宏观应力-应力相关函数与液体的粘度联系起来。原子级应力的概念使得方程中的宏观应力-应力相关函数可以用原子级应力之间的时空相关来表示。分子动力学研究表明，应力-应力相关性具有惊人的长空间延伸，并且在液体中传播的纵波和横波的范围可以超过系统的大小。研究结果表明，剪切波的传播范围与粘度有关的距离范围相对应。因此，我们的结果表明，粘度是一种基本的非局部量。我们还表明，周期性边界条件在分子动力学模拟中起着重要的作用，有效地掩盖了粘度的远程性质。
